1. Field of the Invention
The invention relates in general to holographic storage technology, and more particularly to a data reading method capable of speeding up the decoding.
2. Description of the Related Art
In holographic storage technology, a spatial light modulator (SLM) has been used mainly to encode digital data into a signal beam of light which produces bright and dark spots arranged in a two-dimensional form. The signal beam is then combined with a reference beam to generate an image of an interference pattern (a holographic image or a data page) encoding the original data. The interference pattern is recorded on a storage medium. Any sort of multi-recording method (angle multiplexing, wavelength division multiplexing, phase multiplexing, shift multiplexing, peripheral multiplexing, etc.) can be used to compactly record several data pages layer by layer on the same area (referred to as the data area below) of the storage medium. To read a specific data page, a reference beam of light, which satisfies a particular parameter, is projected onto a data area, generating the signal beam of the data page corresponding to the data area. A light sensing device acquires the signal beam creating an electronic signal which is then decoded to obtain the original digital data.
However, since the optical components inside a holographic storage system may have assembly errors or optical aberrations, an enlargement, contraction, and/or shift may occur, adversely affecting the signal beam that is received by the light sensing device. Therefore, during the encoding process, several reserved block patterns are added to a signal beam as the indicator of a data page. After the light sensing device receives the reconstructed signal image, it searches the pixel data within several pre-determined regions to calculate an accurate position of the reserved block pattern within each of the pre-determined regions and, accordingly, perform suitable image compensation. As a result, the original data on a data page can be decoded and read out correctly. However, in order to cover the reserved block pattern as widely as possible, the pre-determined region cannot be effectively reduced in size, so that the amount of calculation required cannot be reduced, and thereby, not increasing the decoding speed.